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When roof systems are not designed or installed
properly deflection can occur. Deflection is defined as
the bending of wood due to forces, or loads, placed on them.
There are five (5) different types of loads that any structure
must be able to withstand: dead load, live load, shear load,
point load, and spread load. Some of these forces are the
natural result of gravity tugging at the building, dragging
it down. Some are the result of wind gusts, snow loads,
or ground movement.
The type of load refereed to as spread
load is the outward force on walls caused by the downward-and-outward
force of rafters, usually because of heavy snow pressing
down on the roof. If a house isn't prepared to handle this
type of load, it could cave in or suffer partial collapse
or failure. More likely, the framing members will bend under
the loads causing deflection.
When a roof is inadequately supported, the
main ridge board at the peak of the roof, is pushed downward
and the roof rafters push the exterior walls outward. Not
only will the roof from the outside look unsightly, but
also cracks will form on the walls and ceilings, and perhaps
windows and doors will become out of square preventing them
from operating correctly. Dealing with the various loads
that are placed on a house actually means preventing deflection.
Proper building and design practices can prevent the negative
effects on the house by loads.
Older or existing homes run the risk of
being built with practices that are considered to be unsafe
or improper by today's standards. If a roof system is found
to be not supported properly, proper corrective measures
should be taken to prevent deflection.
Many times in older buildings, the ridge
board or peak of the roof is not properly supported causing
displaced spread loads. Additional support posts or columns
are needed to be installed to prevent possible failures
from loads. An adequate and sturdy column can be made with
the use of common 2"X4"s. An example of an adequate support
is by taking two pieces of 2"X4" and nailing them together
to form a corner (see Figure 1). Making the corner is done
to prevent the 2"X4"s from bending or bowing under any extreme
weights. The posts are to be placed in the attic vertically
from the peak of the roof, to the attic floor (see Figure
2). When placing the posts on the attic floor it is extremely
important to place this directly above a load bearing wall.
These columns should be placed under the ridge board approximately
every 4'-5' throughout the attic. Now when a spread load
is placed on the roof, the weight can easily be transferred
through the house as intended.
Many times signs of past problems from spread
loads are detected in homes. It is very important to have
the roof system inspected to confirm if supports were installed
or not, and if they were properly installed.
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